Oil immersed solenoids have been used to control the pressure and flow rate of operating oil flowing through a valve device. One example of the oil immersed solenoids is shown in a longitudinal sectional view of FIG. 6. An oil immersed solenoid 111 is configured such that: a movable core 114 that is movable in an axial direction is provided in a tubular space 122 of a case 117; a fixed magnetic pole portion 113 is provided coaxially with the movable core 114; and an exciting coil 112 is provided at an outer periphery of the fixed magnetic pole portion 113.
According to the oil immersed solenoid 111, by supplying a command electric signal (exciting current) to the exciting coil 112, an attractive force (force in the axial direction) corresponding to the magnitude of the command electric signal is generated at the fixed magnetic pole portion 113. Then, by the attractive force, the movable core 114 is attracted toward the fixed magnetic pole portion 113. A first rod 121 is provided at an axial center portion of the movable core 114. Therefore, the attractive force acting on the movable core 114 can be changed by changing the magnitude of the command electric signal, and with this, an axial biasing force (force in a left direction in FIG. 6) of the first rod 121 can be adjusted (see PTL 1, for example).
For example, the oil immersed solenoid 111 is attached so as to cause a spool (control part) 212 of a valve device 211 to move in the axial direction. Then, the attractive force of the movable core 114 is changed by controlling the command electric signal. Thus, the biasing force of the first rod 121 to push the spool 212 of the valve device 211 in the axial direction is adjusted.
According to the oil immersed solenoid 111, by adjusting the axial biasing force acting on the movable core 114, the spool 212 stops at a position where the biasing force and a force acting from an opposite side of the rod to the spool 212 based on a spring force, an oil pressure, and the like balance. With this, the pressure and flow rate of the operating oil flowing through the valve device 211 are caused to be proportional to the command electric signal.
In reality, it is impossible to produce machined parts constituting the oil immersed solenoid 111 and the valve device 211 such that the same machined parts have the same size. Therefore, the parts are produced within a certain dimensional tolerance range. This dimensional tolerance range is narrow. However, because of this dimensional tolerance, even in the case of using the oil immersed solenoids of the same standard, the axial biasing force acting on the first rod via the movable core by the same command electric signal vary. With this, the force acting on the first rod 121 from the spool 212 also vary. In addition, since an initial biasing force generated when the command electric signal is not supplied differs depending on specifications of hydraulic mechanisms, the initial biasing force needs to be adjustable.
Here, to correct the variations and adjust the biasing force in accordance with the specifications of the hydraulic devices, as in the oil immersed solenoid 111 shown in FIG. 6, an adjusting spring 126 for setting the initial biasing force of the movable core 114, that is, the first rod 121 is provided. In the oil immersed solenoid 111 shown in FIG. 6, the adjusting spring 126 is provided so as to bias the movable core 114 via a second rod 133 in a direction toward the fixed magnetic pole portion 113.
The initial biasing force of the adjusting spring 126 can be adjusted by an adjusting screw 127 provided at one side of the adjusting spring 126, the side being opposite to the movable core side. An axial position of the adjusting screw 127 is adjusted by adjusting a length of thread engagement of the adjusting screw 127. With this, the initial biasing force of the adjusting spring 126, that is, the initial biasing force of the first rod 121 is adjusted.
By adjusting the initial biasing force of the adjusting spring 126 as above, the variations in the force by the dimensional tolerance generated at the time of the production of the parts can be corrected. In addition, the initial biasing force can be adjusted so as to correspond to the specifications of the hydraulic devices.
If air exists in the oil that fills internal spaces 122 and 128 in the oil immersed solenoid 111, damping actions realized by the incompressibility of the oil are spoiled by the compression of the air in the oil, and this may cause, for example, chattering of the movable core 114. Therefore, a degassing operation of the oil in the internal spaces 122 and 128 is performed.
The degassing operation needs to be performed also in a case where the chattering or the like has occurred after the adjustment of the initial biasing force of the adjusting spring 126.
Here, in the above conventional art, after the initial biasing force of the adjusting spring 126 is adjusted by the adjusting screw 127, the degassing operation of loosening a degassing plug 156 together with the adjusting screw 127 to remove the air and air bubbles existing in the internal spaces 122 and 128 together with the oil is performed. After that, by tightening the degassing plug 156 back to the original position, the adjusting spring 126 can be returned to the state realized after the above adjustment.